Make sure you read this:
Long story short, if you have an unclean shutdown, there's a good chance you will be going through an initial sync again. 4TB and a 2.6 Mil files took (pulling from memory) about 4 days. It will be a lot slower if you have slow spindles in your file servers since it has to stage all the files first.
Also, all the files that changed during the unclean shutdown sync on the "unclean shutdown" server will get overwritten with remote files since they will take priority.
DFS is pretty great, but just be aware of the caveats! (and this is not the only one)